The present invention relates to a drying cylinder for use in paper making, and more particularly to a drying cylinder comprising a built-up insulating sheet fixedly wound around the circumferential surface of the drying cylinder at the appointed positions thereof in order to control the moisture profile of paper webs in the cross machine direction thereof in a paper making process.
In cases where wet paper web is subjected to a drying treatment in a multi-cylinder type drying machine for use in paper making, it is remarkably important to equalize the moisture profile of the paper web in the cross machine direction thereof. If the moisture profile of the paper web is not equalized in the cross machine direction thereof, drying streaks are produced on the final products which lead to the generation of various kinds of defect such as curling in following stage.
It is, however, considerably difficult from a practical point of view to equalize the moisture profile of paper web in the cross machine direction thereof on account of the defects produced in the preceding process and inevitable causes incidental to the drying process. Thus, a large number of technical means for improvements of a drying cylinder in heat-conducting structure and a dryer felt have been proposed and practiced in order to prevent wet paper web from being non-uniformly dried in the drying part of a paper making process. For example, the present applicant already proposed a technical means of remarkably reducing the fluctuation in the moisture profile of paper web in the cross machine direction thereof in comparison with known means for the prevention of non-uniform drying in U.S. patent application Ser. No. 622,483 filed Oct. 19, 1984 and titled "Method of controlling moisture profile in paper web in paper drying process and apparatus for practicing same". The preceding invention proposes a means for eliminating a non-uniform moisture profile in wet paper web, which is transferred into a drying part, in the cross machine direction thereof, in which synthetic fabrics containing air-holding portions therein are fixedly wound around the surface of a drying cylinder at the desired positions thereof to make the air-holding portions function as insulting layers and lower heat conducting temperature of the surface of the drying cylinder contacting with fixedly wound layers of the synthetic fabrics, whereby a uniform drying condition is ensured all over the width of the wet paper web.
The following methods can be given as a means for fixedly winding such insulating sheets around the surface of a drying cylinder at the appointed positions thereof.
The first is a method in which synthetic fabrics provided with joints are wound around the circumferential surface of a drying cylinder at the desired positions thereof, the synthetic fabrics being jointed at end portions thereof through the joints.
The second is a method in which the same synthetic fabrics, which function as insulating layers, provided with joints as used in the first method are wound around the surface of a drying cylinder at the desired positions thereof and then the joint portions are adhered to the synthetic fabrics by adhesive agents all over the width thereof and simultaneously edge portions of the synthetic fabrics are adhered to the drying cylinder spot by spot.
The third is a method in which the same synthetic fabrics as in the above described method are wound around the surface of a drying cylinder at the desired positions thereof and then edge portions of the synthetic fabrics are fixed by means of a narrow adhesive tape having a resin coated layer on the surface thereof.
The fourth is a method in which the same synthetic fabrics as in the above described method are wound around the surface of a drying cylinder at the desired positions thereof and then the synthetic fabrics is fixed by means of adhesive tapes, which are slightly wider than the synthetic fabric and have a resin coated layer on the surface thereof, all over the surface of the wound synthetic fabrics.
However, all of these methods have some disadvantages in respect of practical use. That is to say, since a paper making machine is a large-sized machine having a width of 3 to 10 m, a drying cylinder having a large diameter of 1.2 to 1.8 m, several drying cylinder being contained in one set of paper making machine, and a workfield, where synthetic fabrics functioning as insulating materials are fixedly wound around the circumferential surface of a drying cylinder, is generally disadvantageous in footing, narrow and often insufficient in lighting, it requires considerable skill and long working time to ensure the operation of fixedly winding the synthetic fabrics around the circumferential surface of the drying cylinder at the desired positions thereof. For example, in cases where insulating layers formed of synthetic fabrics are formed on the circumferential surface of a drying cylinder, it is necessary that the synthetic fabrics are cylindrically joined warp-loop joints formed at the end portions of the synthetic fabrics and inserting a thin wire through the interdigitate loops. However, since the warp-loop joints formed at the end portions of thin synthetic fabric have a small diameter and dense loops, through which a wire is inserted, and also the wire is thin, it requires considerable skill and long working time to ensure the operation of fixedly winding the synthetic fabrics around the circumferential surface of a drying cylinder at the desired positions thereof, whereby the disadvantages such as a considerably long preparatory time taken until the operation is started and the lower operating rate of a paper making machine were produced according to circumstances.